Prostanoids are a family of eicosanoids that comprise prostaglandins (PGs), prostacyclins (PGIs), and thromboxanes (Txs). Their receptors belong to the G-protein coupled receptor (GPCR) superfamily of receptors and may be grouped into five classes, namely, prostaglandin D (DP), prostaglandin E (EP), prostaglandin F (FP), prostaglandin I (IP), and Thromboxane A (TP) based on their sensitivity to five naturally occurring prostanoids, PGD2, PGE2, PGF2[alpha], PGI2, and TxA2, respectively (Coleman, R. A., 2000).
Prostaglandins contribute to the sensitization of peripheral and central nociceptive neurons during peripheral inflammation (Dirig and Yaksh, 1999) and play an important role in the pathogenesis of neuropathic pain following nerve injury (Syriatowicz et al 1999; Kawahara et al, 2001; Samad et al, 2002; Ma and Eisenach, 2003; Durrenberger et al., 2006).
Prostaglandin E2 (PGE2) is considered to be the dominant pro-nociceptive prostanoid. Guay and colleagues, analyzing the concentrations of different prostaglandins in the cerebrospinal fluid, found that PGE2 was the most prevalent prostanoid and exhibited the highest increase after peripheral carrageenan-induced inflammation (Guay et al., 2004). PGE2 is generated in most cells in response to mechanical, thermal or chemical injury and inflammatory insult, resulting in sensitization or direct activation of nearby sensory nerve, endings. Its production requires the activity of at least one of the two cyclooxygenase isoforms, COX-1 constitutively expressed or COX-2 which is inducible and particularly relevant for inflammation-induced PGE2 formation. Therefore, non-selective inhibitors of COX-1 and COX-2, and selective COX-2 inhibitors provide good pain relief. However, the long-term use is associated with gastrointestinal or cardiovascular side effects, respectively.
Downstream components of the inflammatory cascade could be an alternative approach for the treatment of the PGE2 associated pain. PGE2 binds to four different G-protein coupled receptors named EP1, EP2, EP3 and EP4 (Narumiya et al., 1999).
Studies employing antagonists suggest that blocking EP1, EP2, EP3 or EP4 receptors may reduce certain types of pain (Oka et al. 1997; Omote et al., 2002; Lin et al, 2006) and agonists increase nociceptive responses (Minami et al., 1994). Among these PGE2 receptor subtypes, most of drug discovery studies have focused on the EP1 receptors (Hall et al., 2007).
EP1 receptor stimulation mediates increases in intracellular calcium ions, facilitating neurotransmitter release (Asboth et al., 1996). EP1 receptor is preferentially expressed in primary sensory neurons, including their spinal cord terminals (Oidda et al., 1995) although it is also distributed in other tissues (Breyer et al., 2000; Schlötzer-Schrehardt et al., 2002). In the brain, marked differences in the level of EP1 expression among the cerebral regions were found. The strongest levels of EP1 mRNA were found in parietal cortex and cerebellum, followed in descending order by frontal cortex and striatum. The hypothalamus, hippocampus and brain stem displayed a low-level EP1 mRNA signal (Candelario-Jalil et al., 2005). In the spinal cord, several studies have reported the effects of PGE2 on neuronal excitability or synaptic transmission (Baba et al., 2001) and pain transmission (Nakayama et al., 2004). Therefore, EP1 receptor antagonists, blocking the positive feedback cascade mediated by PGE2, may result in analgesic efficacy. In this regard, using EP receptor deficient mice, a prominent contribution of EP1 receptors has been described (Minami et al., 2001). EP1−/− knockout mice demonstrated a role of this receptor in mediating peripheral heat sensitization after subcutaneous PGE2 injection (Moriyama et al. 2005; Johansson et al. 2011), and EP1 receptor antagonism has been reported to reduce mechanical hyperalgesia in nerve injured rats (Kawahara et al., 2001), in the carrageenan model (Nakayama et al. 2002), or in the incisional model of postoperative pain (Omote et al 2002). Moreover, EP1 antagonists demonstrated analgesic activity in a complete Freund's adjuvant model of knee joint arthritis (Giblin et al, 2007; Hall et al, 2009). It has also been reported that the contribution of PGE2 in human visceral pain hypersensitivity is mediated through the EP1 receptor (Sarkar et al., 2003).
In addition to being useful for modulating pain, EP1 antagonists may also be useful for the treatment or prevention of other EP1 receptor-mediated diseases such as motility-related disorders including gastrointestinal disorders, urinary incontinence and other urinary tract diseases; dysmenorrhea; preterm labour; diabetic retinopathy; tumour angiogenesis; cancer; metastatic tumour growth; neurodegenerative diseases including senile dementia, Alzheimer's disease, Pick's disease, Huntington's chorea, Parkinson's disease, Creutzfeldt-Jakob disease, or amyotrophic lateral sclerosis; neuroprotection/stroke; glaucoma; osteoporosis; bone fractures; Paget's disease; hyperthermia including different types of fever as rheumatic fever; symptoms associated with influenza or other viral infections; gastrointestinal disorders related with chemotherapy or irritable bowel syndrome; gastrointestinal bleeding; coagulation disorders including anaemia, hypoprothrombinemia, haemophilia or other bleeding problems; kidney diseases including nephritis, particularly mesangial proliferative glomerulonephritis and nephritic syndrome; thrombosis and occlusive vascular diseases.
In turn, EP1 receptor agonists also may have a number of utilities. These include, but are not limited to treatment of influenza, bone fracture healing, bone disease, glaucoma, ocular hypertension, dysmenorrhoea, pre-term labour, immune disorders, osteoporosis, asthma, allergy, fertility, male sexual dysfunction, female sexual dysfunction, periodontal disease, gastric ulcer, and renal disease. EP receptor agonists may also be useful for expansion of hematopoietic stem cell populations.
Based on the above mentioned results coming from animal and human studies, EP1 receptor has been identified as a selective target for the development of new potential therapies for the treatment of those disorders where PGE2 action is involved. In view of the potential therapeutic applications of agonists and antagonists of the EP1 receptor, a great effort is being directed to find selective ligands. Despite intense research efforts in this area, very few compounds with selective EP1 activity have been reported.
There is thus still a need to find compounds having pharmacological activity towards the EP1 receptor, being both effective and selective, and having good “druggability” properties, i.e. good pharmaceutical properties related to administration, distribution, metabolism and excretion.
The present invention hereby provide some novel compounds complying with the above mentioned properties.